Wind tunnel fabrication method



Aug. 11, 1970 A. FERRI v WIND TUNNEL FABRICATION METHOD 2 Sheetsj-Sheet 1 Original Filed May 11,

INVENTOR. //vro/v/o FZWRV M3, H w-s 8, .Sg/fmd ATTORNEY Au -11 1970 A.1=ER| 3,523,350

Original Filed May 11, 1965 2 Sheets Sheet 1 INVENTOR #wrawo 36W 1 M, m a ,W

ATTORNEYS.

United States Patent 3,523,350 WIND TUNNEL FABRICATION METHOD Antonio Ferri, Rockville Centre, N.Y., assignor to General Applied Science Laboratories, Inc., Westbury, N.Y., a corporation of New York Original application May 11, 1965, Ser. No. 454,837, now Patent No. 3,353,405, dated Nov. 21, 1967. Divided and this application Sept. 28, 1967, Ser. No. 703,487

Int. Cl. B21d 53/00 U.S. Cl. 29-157 2 Claims ABSTRACT OF THE DISCLOSURE A relatively inexpensive method of fabricating a hypersonic wind tunnel. The nozzle of the tunnel is formed as a separate unit composed of rectangular blocks with beveled edges which form deep grooves when the blocks are assembled together. The grooves are filled with weld material, and the assembled structure is machined into a cylindrical shape. A matching cylindrical hole is cut into a mounting block, and the nozzle unit then is secured in the hole. Then, a frusto-conical inlet section is machined into the mounting block and nozzle unit assembly. The diverging portion of the tunnel preferably is of divergingparallel shape, and is formed by shaping the edges of a first pair of flat elongated plates so as to have the desired contour, forming a pair of ledges on a second pair of flat elongated plates, the ledges having a pattern with the same contour as the first plates, fitting the plates together with the edges of the first plates against the ledges of the second plates, and bending both sets of plates and securing the plates together This application is a division of application Ser. No. 454,837, filed May 11, 1965, and now Pat. No. 3,353,405.

The present invention relates to gas-accelerating nozzles such as nozzles used in wind tunnels, and to methods of fabricating such nozzles.

Wind tunnels are structures for creating high-speed gas streams in which aerodynamic bodies such as models of missiles and aircraft wings are placed and tested. The model tested in this manner is subjected to forces similar to those to which the full-size aerodynamic body would be subjected if it were in actual flight.

Most wind tunnel nozzles create a high-speed gas stream by supplying a compresed gas, usually air, to a converging-diverging nozzle which accelerates and expands the pressurized gas, and forms it into a high-speed gas stream. The converging-diverging nozzle usually comprises an inlet section whose cross-sectional area decreases in the direction of flow through the nozzle, and a diverging outlet section, usually of relatively great length, whose cross-sectional area increases in the direction of flow through the nozzle, with a throat joining the converging and diverging sections.

As is well known in the high-speed gas dynamics art, the speed ultimately attained by the gas accelerated in a well-designed converging-diverging nozzle depends upon the area ratio of the nozzle, ie the ratio of the crosssectional area of the nozzle passageway at its exit to the cross-sectional area at its throat. Thus, by pre-selecting the area ratio of the nozzle, the ultimate speed of the gas can be made transonic (slightly greater or less than Mach 1, the speed of sound in air), or supersonic (substantially greater than Mach 1), or hypersonic (very much greater than Mach 1).

In testing modern rocket and aircraft designs, often it is necessary to produce gas streams of hypersonic velocity; for example, gas streams having a speed of around Mach 12. In order to produce such extremely high speeds the area ratio of the nozzle must be very high. A high area ratio usually is attained by making the throat area as small as possible rather than by making the exit area larger in order to make the wind tunnel test section of reasonable size and as inexpensive as possible, and in order to minimize the quantity of gas flow through the nozzle and thus minimize the required capacity of the system used to supply compressed gas to the wind tunnel.

Another feature which often is provided in wind tunnel nozzles is a contoured diverging nozzle section. The walls of such contoured sections first diverge and then charge gradually to become parallel to the longitudinal axis of the nozzle. The parallel-wall portion of the nozzle section straightens the gas flow and substantially removes radially-directed flow components so that aerodynamic bodies tested in this portion of the nozzle will not be subjected to the test errors that the radial components might induce.

Several different prior art wind tunnel nozzles are known, but all such nozzles have distinct disadvantages which are greatly magnified when hypersonic-speed gas streams must be produced.

One of these prior art nozzles has frnsto-conicallyshaped converging and diverging sections. One serious problem with this prior art nozzle is that if the wind tunnel is of even moderate size, the cost in materials and labor for machining the conical sections of such a structure is extremely high. What is more, unless complicated and very costly machining techniques are used to form a contour in the diverging section of the nozzle, the nozzle will produce radial gas flow components which are undesirable for aerodynamic testing.

Another prior art nozzle is the so-called two-dimensional nozzle. Such a nozzle typically comprises two long, parallel, flat metal side-plates between which are welded a pair of contoured top and bottom plates. This nozzle has a rectangular cross-sectional shape. The contour in the top and bottom plates can be provided by expensive machining so as to produce a fixed-Mach-number nozzle, or can be provided by using relatively thin top and bottom plates whose contours can be adjusted by use of hydraulic jacks so as to produce a variable- Mach-number nozzle.

A serious problem with both of these varieties of twodimensional nozzles occurs when the cross-sectional area at the throat is minimized in order to maximize the area ratio of the nozzle. Since the nozzles side plates are parallel, the throat area is minimized by making the spacing between the top and bottom plates at the throat extremely small. For example, in a typical nozzle two feet wide and having an exit opening height of two feet, the throat height or spacing might be only a few hundredths of an inch. This requirement for an extremely small throat height means that the top and bottom plates must be extremely flat and parallel to one another at the throat in order to prevent distortions in the gas flow through the nozzle. At such close spacings between the plate, even the slightest bulge, curve or nick in either of the plates is likely to cause substantial distortion.

In view of the above discussion, it is an object of the present invention to provide a wind tunnel nozzle and construction method which avoid all of the above-mentioned problems and yet are relatively inexpensive. Thus, it is an object of the present invention to provide relatively inexpensive wind tunnel nozzle structures and similarly inexpensive fabrication methods, with the nozzles being capable of producing gas streams with substantially parallel flow without distortion due to small imperfections at its throat.

The drawings and description that follow describe the invention and indicate some of the ways in which it can be used. In addition, some of the advantages provided by the invention will be pointed out.

In the drawings:

FIG. 1 is a partially cross-sectional and partially broken-away plan view of a wind tunnel nozzle constructed in accordance with the present invention;

FIG. 2 is a partially broken-away cross-sectional view taken along line 2-2 of FIG. 1;

FIG. 3 is a partially broken-away view of the nozzle shown in FIG. 2 looking into the exit end of the nozzle towards the nozzles inlet end;

FIG. 4 is a partially-schematic enlargement of a portion of the structure shown in FIG. 1;

FIG. 5 is an exploded view of a portion of the structure shown in FIG. 4 as it appears during fabrication; and

FIG. 6 is a partially-schematic view of the structure shown in FIG. 5, after assembly.

In FIGS. 1 through 3 of the drawings is shown a wind tunnel nozzle 10 constructed in accordance with the present invention. As is shown in FIG. 1, nozzle 10 includes a throat section 12, a straight diverging section 14, and a contoured diverging section 16. Near the end of contoured section 16 is a test section 18 in which aerodynamic models can be placed for testing. The models can be viewed through side-windows 20 and 22. The cross-sectional shape of the nozzle 10 is square everywhere except in the converging portion of throat section 12. The converging section is frusto-conical and has a circular cross section.

Highly compressed air or some other appropriate gas or combination of gases is supplied to the inlet opening of throat section 12 and typically is accelerated by the nozzle 10 to a hypersonic velocity of around Mach 12 in the test section 18. The contour of contoured diverging section 16 is diverging-parallel; that is, section 16 first diverges and then gradually changes to a shape Which produces substantially parallel gas flow in test section 18.

Referring now to FIG. 4 as well as FIGS. 1 and 2, the throat section 12 of nozzle 10 includes a cylindrical mounting block 24 in which is mounted a throat structure 26 and the ends of four metal plates 28, 30, 32 and 34 which form the walls of the straight diverging section 14 of the nozzle 10.

As is shown in FIGS. 5 and 6, the throat structure 26 is composed of four metal blocks; top and bottom blocks 36 and 38, and left and right side blocks 40 and 42. The four blocks 36, 38, 40 and 42 originally are rectangular in shape; they are machined and drilled so as to have the forms shown in FIG. 5. Then they are assembled together so as to form a nozzle structure having a straightwalled throat 44 and a smoothly-diverging outlet section 46, each having a square cross-sectional shape.

The diverging outlet section 46 is formed by machining a gradually-sloping beveled portion 48, 50, 52 or 54, respectively, at one end of each block. Each of these beveled portions has the same length and slope. Side blocks 40 and 42 are machined further so as to have identical outwardly-sloping surfaces at the top and bottom. The slope and length of each of these surfaces are made equal to the slope and length of each beveled portion 48, 50, 52 and 54 so that the beveled portions of the blocks fit together tightly when assembled.

Certain of the outside edges of each block are machined to give each edge a relatively steep beveled portion such as beveled edge portions 56, 58, 60 and 62, so as to form deep V-shaped notches at the external joints between the blocks when they are assembled as shown in FIG. 6.

The four blocks then are assembled by means of four pins 64 which are press-fitted into holes in the blocks, with the side blocks 40 and 42 sandwiched between the top and bottom blocks 36 and 38. The outwardly-flaring top and bottom surfaces of side blocks 40 and 42 fit snugly against beveled portions 48 and of top and bottom blocks 36 and 38 to form a smooth gas passageway through the throat structure 26 without spaces between adjacent blocks. Then, the deep V-shaped grooves shown in FIG. 6 are filled with weld material so as to weld and further secure the four blocks together.

The mounting block 24 must serve as a housing for the throat structure and must be capable of withstanding the high pressure of the compressed gas it receives. Therefore, housing 24 must have relatively thick walls. This fact, together with the rectangular shape of structure 26, makes it difiicult to mount the throat structure in the housing. However, this problem is solved rather simply and inexpensively by boring a cylindrical cavity in one end of the block 24 and shaping the exterior of structure 26 to fit into the cavity.

Referring now to FIG. 6, the throat structure 26 is machined from its original rectangular shape (shown in dashed lines) to the cylindrical shape shown in full lines. Advantageously, since the original V-shaped Welds were made quite deep, considerable weld material remains after this machining operation so as to continue to aid in securely holding the four blocks together. The cylindrical throat structure 2-6 then is fitted into the cylindrical cavity in mounting block 24 and is Welded in place.

Referring now to FIG. 4, a smooth frusto-conical flared inlet opening 65 is formed in the end of housing 24 opposite the end in which throat structure 26 is secured. This opening 66 is formed by a relatively easy machining step, and extends partially into throat structure 26 so as to give structure 26 a frusto-conical inlet opening which merges smoothly with the square cross-sectional throat 44. The joint between throat structure 26 and mounting block 24 is quite smooth since it is shaped in the machining of inlet opening 66. Note that the outlines of mounting block 24 and structure 26 before the inlet opening is machined are shown as dashed lines in FIG. 4.

Referring now to FIGS. 1 and 2 as well as FIG. 4, the four plates 28, 30, 32 and 34 are assembled together to form the straight diverging section 14. Their smallest ends then are machined to a cylindrical form at the surface indicated by numeral '68 in FIG. 4 and the cylindrical ends are inserted into another cylindrical cavity in the exit end of block 24 so as to insure that they fit properly. 'Plates 28, 30, 32 and 34 are made relatively thick so that there will be sufficient material remaining in the small ends of the plates after they have been machined. The four plates 28, 30, 32 and 34 then are disassembled. Next, the ends of relatively thin top and bottom contour plates 70 and 72 are welded, respectively, to plates 32 and 34 at joints 74 and 76 (see FIG. 2). Then the top and bottom plates 32 and 34 are reinserted into the cylindrical opening in block 24, and are welded in place.

As is shown in FIG. 1, top and bottom plates 70- and 72 are cut in a contoured outline such as to give the diverging contoured nozzle section 16 the diverging parallel shape desired. These relatively thin top and bottom plates may be cut to shape relatively easily and inexpensively by conventional techniques.

Next, two non-contoured side-plates 78 and 80 are cut out of fiat metal having approximately the same thickness as the top and bottom plates 70 and 72. Holes are cut for viewing windows 20 and 22, and metal blocks 82 are welded to the side plates 78 and 80 along contour lines the same as those of the edges of the top and bottom plates 70 and 72.

After that, side plates 78 and 80 are welded at their small ends to plates 28 and 30 at joints 84, 86 respectively (see FIG. 1). Plates 28 and 30 are reinserted in the cylindrical opening at the end of block 24 and are welded in place and to the top and bottom plates 32 and 34 to complete the straight diverging section 14 of the nozzle 10.

Following these steps, all four plates 70, 72, 78 and 80 are bent to conform to one another. Bending pressure is applied to top and bottom plates 70 and 72 -by hydraulic jacks acting in the directions of the arrows shown in FIG. 2 so as to force the top and bottom plates against the blocks 82 on side plates 78 and 80. Simultaneously, bending pressure is applied to side plates 78 and 80 by means of other hydraulic jacks acting in the directions of the arrows in FIG. 1 to bend the side plates to conform to the contour of the edges of the top and bottom plates 70 and 72. Then the top and bottom plates are welded to the blocks 82, and various side-braces 88 are welded to this structure, as are an end support plate 90 and a relatively thick support plate 92 at the end of straight diverging section 15.

It should be understood that the application of bending pressure and welding of the plates to the blocks 82 advantageously is performed step-by-step in relatively short lengths starting at the small end and Working towards the large end of section 16.

The advantages of nozzle 10 over known wind tunnel nozzles truly are notable. The throat 44 of the nozzle is symmetric with respect to its longitudinal axis so that the cross-sectional area of the throat may be made quite small without making either the height or width of the throat of disproportionate size. Thus, the distortion problems of the usual prior art two-dimensional nozzle described above are avoided.

Further avoidance of the distortion problem is provided by forming the throat structure 26 as a separate unit by means of the above-described method. By using this structure and method, the components of the throat structure 26 are made small enough to allow them to be machined and finished with great accuracy at a relatively low cost.

The nozzle 10 is considerably easier to maintain and modify than prior art nozzles. If the throat walls are damaged or worn, the whole structure 26 may be replaced Without having to replace the other expensive components of the nozzle 10. What is more, the area ratio of the nozzle 10 and consequently the test section Mach number may be changed by replacing the throat structure 26 with another having diflerent throat dimensions.

Most impressively, the nozzle 10, when constructed by the above-described method, costs only about one-third as much to make as the next-best type of nozzle giving similar performance.

The above description of the invention is intended to be illustrative and not limiting. Various changes or modifications in the embodiments described may occur to those skilled in the art and these can be made without departing from the spirit or scope of the invention as set forth in the claims. For example, it is possible to weld plates 28, 30, 32 and 34 into block 24 in any sequence desired. Similarly, the sequence of steps used in assembling plates 28, 30, 32 and 34 With plates 70, 72, 78 and 80 may be varied as desired without departing from the spirit or scope of the invention.

I claim:

1. A method of fabricating from substantially rectilinear blocks a gas-accelerating nozzle having throat and diverging gas passageway sections with substantially rectilinear cross-sectional shapes, said method comprising the steps of shaping said blocks to fit together and form said passageways, forming relatively deep grooves at the external junctures between said blocks, filling at least the bottom portions of said grooves with weld material, and machining the rectilinear structure so formed to give it an external cylindrical shape, said grooves being so deep that at least the bottom portion of the weld material in said grooves remains after said structure has been machined to a cylindrical shape.

2. A method as in claim 1 including the step of providing a mounting housing capable of withstanding relatively high gas pressures, forming a cylindrical cavity in said housing, and securing said gas-accelerating nozzle in said cavity.

References Cited UNITED STATES PATENTS 2,332,407 10/1943 Spenle 138-44X 2,696,110 12/1954 Eggers 73-147 3,249,989 5/1966 Robinson 29-457 JOHN F. CAMPBELL, Primary Examiner D. C. REILEY, Assistant Examiner US. or. X .R, 2 -431; 

